1. Field of the Invention
The present invention relates to a substrate holding device for holding a substrate such as a semiconductor wafer or a glass substrate for a liquid crystal display device, and a substrate processing apparatus comprising the same.
2. Description of Related Art
A single substrate processing apparatus used in the manufacturing process of a semiconductor device, for example, comprises a spin chuck for holding a substrate almost horizontally and rotating the held substrate, and a nozzle for supplying a process liquid such as a chemical liquid to the substrate held in the spin chuck. In the single substrate processing apparatus, process of the substrate using the process liquid is achieved by supplying, while rotating the substrate within a horizontal surface using the spin chuck, the process liquid from the nozzle to the substrate that is being rotated.
The spin chuck comprises a rotating shaft arranged in a vertical direction, a spin base mounted on an upper end of the rotating shaft almost horizontally, and a plurality of chuck pins arranged on an upper surface of the spin base. The rotating shaft is integrated with a driving shaft of a motor. The rotating shaft is rotated by the motor with the substrate held by the plurality of chuck pins, so that the substrate, together with the spin base, is rotated.
The motor is surrounded by a cylindrical cover member. In order to prevent a corrosive atmosphere including a process liquid component from reaching to a rotation mechanism section including the motor or the like and prevent an atmosphere including dust (particles) generated from the rotation mechanism section from reaching to the substrate, an upper end of the cover member leads to the vicinity of a lower surface of the spin base, and a sealing mechanism is arranged between the upper end of the cover member and the lower surface of the spin base.
It is considered that a contact seal such as an oil seal is used, for example, for the sealing mechanism. However, the contact seal may cause generation of dust and reduction in sealing properties by abrasion. Since the diameter of the cover member surrounding the motor is relatively large, the diameter of the contact seal provided along the upper end of the cover member also becomes large. When the spin base is rotated, therefore, the peripheral speed of a contact portion with the contact seal on the lower surface of the spin base is increased so that the contact seal may be baked.
In order to avoid such a problem caused by using the contact seal, a so-called non-contact static pressure-type seal may, in some cases, be used. The non-contact static pressure-type seal comprises a fixed ring supported on an upper end surface of the cover member through a plurality of springs, and a rotating ring mounted on the lower surface of the spin base and arranged opposite to the fixed ring. A plurality of clean gas blow-off ports open to an upper surface of the fixed ring. Clean gas can be supplied to a space between the fixed ring and the rotating ring from the clean gas blow-off ports. In a state where no clean gas is supplied from the clean gas blow-off ports, the fixed ring is abutted against the rotating ring over its entire periphery by the urging force of the springs. When clean gas is supplied to a space between the fixed ring and the rotating ring from the clean gas blow-off ports, the fixed ring is spaced apart from the rotating ring by several micrometers to tens of micrometers by the pressure (static pressure) of the clean gas, thereby entering a non-contact state. At this time, the clean gas supplied to the space between the fixed ring and the rotating ring branches off to flow along the inside and the outside of the cover member from the space. Consequently, sealing between the fixed ring and the rotating ring is achieved.
While the substrate (spin base) is being rotated, the clean gas continues to be supplied to the space between the fixed ring and the rotating ring in order to maintain the non-contact state between the fixed ring and the rotating ring. However, the flow rate of the clean gas supplied to the space between the fixed ring and the rotating ring may be reduced due to a failure in a clean gas piping system or a clean gas supply source, for example. When the flow rate of the clean gas is reduced, the pressure of the clean gas between the fixed ring and the rotating ring is reduced, whereby the rotating ring rotates while coming into contact with the fixed ring. Therefore, the fixed ring and/or the rotating ring may be damaged, and atmospheric contamination with abrasion powder of the fixed ring and/or the rotating ring may be occurred. Even if interlocking control for stopping the driving of the motor to stop the process of the substrate in response to the reduction in the flow rate of the clean gas is carried out, the rotating ring rotates while coming into contact with the fixed ring for approximately three seconds from the stop of the driving of the motor to the stop of the rotation of the spin base. Therefore, the same problem occurs. When such a problem occurs, cleaning for removing the abrasion powder must be performed in addition to the repair of a faulty portion. As a result, a down time period (a time period during which the substrate cannot be processed) by the substrate processing apparatus is lengthened.
In a configuration using a non-contact static pressure-type seal, the clean gas must continue to be supplied to the space between the fixed ring and the rotating ring while the substrate is being rotated. Therefore, the running cost is high.